US2537767A - Phase shifting control circuit - Google Patents

Description

1951 D. F. LANGENWALTER 2,537,767

PHASE SHIFTING CONTROL CIRCUIT Filed Sept. 25, 1948 Fig.\.

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I 0 90 I80 DEGREES FROM FULL ON Daniel F Langenwalter;

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Patented Jan. 9, 1951 PHASE SHIFTING CONTROL CIRCUIT Daniel F. Langenwalter, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application September 25, 1948, Serial No. 51,251

3 Claims. 1

This invention relates to control systems for deriving a voltage from a source of periodically varying voltage and for shifting the phase of the derived voltage with respect to the voltage of the source, and an object of the invention is the provision of a simple, sensitive, reliable and inexpensive control system of this character.

The invention is well adapted for use in connection with electric valves such as thyratrons. In control systems in which such electric valves are used, the conduction of the valve is usually controlled by shifting the phase of the voltages applied to the control grids with respect to the anode voltages.

A further object of the invention is the provision of a phase shifting circuit which will maintain a negative bias voltage which is equal to at least three times the maximum value of the negative critical grid voltage.

Another object of the invention is the provision of a phase shifting circuit which produces a voltage with a very steep wave front for all phase angles of the phase shifted voltage within 180 of the voltage of the source and which is positive for approximately 90 and negative for approximately 270 of each cycle.

In carrying the invention into effect in one form thereof a bridge circuit is provided. Two adjacent arms of the bridge are inductive impedances. A third arm comprises a capacitative reactance element and the reactance winding of a saturable reactor connected in series, while the fourth arm comprises a resistance and a capacitor connected in parallel.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to the accompanying drawing, of which Fig. 1 is a simple diagrammatical sketch of an embodiment of the invention; Fig. 2 is a chart of characteristic curves which illustrate operation of the invention, and Fig. 3 is a diagrammatical sketch corresponding to a portion of the circuit of Fig. 1 showing a modified form of the invention.

Referring now to the drawing, there is illustrated a pair of thyratrons I and 2 arranged in a system for transmitting energy from an alternating voltage source 3 to a direct current circuit l. The anodes I a and 2a of the thyratrons are connected to opposite terminals of the secondary winding of a transformer 5 of which the primary winding is connected to the source 3. The electrical midpoint of the secondary wind- 8 is connected to the conductor 6 which thus becomes the negative supply conductor of the direct current circuit and the cathodes lb and 2b are connetced to the conductor 1 which becomes the positive supply conductor. Control of the current conducted by the thyratrons is effected by supplying to the grids lo and 20 a periodically varying voltage having the same periodicity as the anode voltage and by shifting the phase of the grid voltage relative to the anode voltage.

For this purpose a grid voltage phase shifting circuit is provided. It comprises a transformer 8 having its primary winding 8a connected to the source 3 and a secondary winding having two sections 8b and 80 connected in series relationship. Each of the sections contains inductive impedance and each section constitutes an arm of a bridge circuit. A third arm of the bridge comprises the reactance winding 9a of a saturable core reactor 9 connected in series with a capacitor III which is connected in parallel with a resistor II. The fourth arm of the bridge comprises a capacitor l2 and a resistor iZa.

Between the opposite diagonal points l3 and it of the bridge is connected the output circuit which comprises the primary windings Ho and Ilia of transformers l5 and I6. As shown, the two primary windings are connected in series relationship with each other. Across the outside terminals of the primary windings is connected a parallel circuit which comprises two oppositely poled rectifiers l1 and is connected in series relationship. These rectifiers may be of any suitable type. Preferably they are the well known selenium rectifiers.

The secondary windings I51) and I6?) of transformers l5 and it are also connected in series relationship. The upper terminal of secondary winding i5b is connected through a resistor l9 to the grid |c of thyratron I and the lower terminal of secondary winding lBb is connected through a resistor 20 to the grid 20 of thyratron 2. Between the junction point of the secondary windings I5b and I61) and the common cathode lead I is connected a resistor 2| and a grid bias capacitor 22 in parallel therewith.

The capacitance of capacitor in is chosen to provide resonance between the capacitor Ill and the reactance winding 9a of the saturable reactor when the reactor is approximately per cent saturated. 1

With the foregoing :funderstanding of the elements, the operation on the phase shifting circuit will readily be understood from the following description.

In the chart of characteristic curves illustrated in Fig. 2, the alternating voltage which is supplied to the primary winding 8a of the transformer and the voltage which is induced in the secondary windings 8b and 8c is represented by the curve 23.

With the saturable reactor 9 unsaturated, i. e. with zero direct current flowing in the saturating winding, a periodically varying voltage having both positive and negative values in each cycle appears across the output terminals l3 and M. This voltage is applied to the primary windings I50. and 16a. During the half cycle of this voltage in which the upper terminal of the primary winding is positive, current flows through the primary winding [a, resistor 24 and rectifier l8. Resistor 24 is of relatively low resistance and consequently primary winding 3a is effectively short-circuited by the rectifier during this half cycle. During the next half cycle current flows through primary winding [6a, resistor 24 and rectifier l1, and primary winding l5a is efiectively short-circuited by rectifier l'l. Thus the current which flows in the primary windings a and Na is rectified and has a direct component.

This direct current component is eliminated from the voltage which is induced in the secondary windings since a direct current component cannot pass through a transformer. Consequently the rectified half wave currents in pri- 1.

mary windings Mia and lfia cause alternating ing voltages to be induced in the secondary winding which are unsymmetrical about the zero axis.

For example, with zero direct current flowing in saturating winding 9b the voltage induced in secondary winding 65a during one cycle of the alternating voltage applied to the primary winding results in a grid voltage between grid lo and cathode lb of thyratron i which is represented by the curve 25 in Fig. 2. It will be noted that this voltage lags the input voltage approximately 180 electrical degrees. Further, it will he noted that this phase shifted voltage is unsymmetrical about the zero axis and that it is positive for approximately 90 and negative for approximately 270. A voltage of similar wave shape but of opposite phase will be induced in the secondary winding Nib.

An increase in the direct current flowing in the saturating winding 9b of the reactor, e. g. an increase to one milliampere produces a phase shift of the voltage, i. e. a phase advance. The phase shifted voltage for this degree of saturation of the reactor is represented by the curve 26. It will be noted that the phase shifted voltage as represented by curve 26 has a very steep wave front. A voltage with a steep wave front is highly desirable as a grid voltage for thyratrons since it causes the thyratron to fire invariably at the same phase angle in each positive half cycle of anode voltage. In addition, it will be noted that the voltage represented by the curve 26 has a relatively high peak value. In the embodiment described, its positive maximum voltage is approximately 200 volts. This also is advantageous in tryratron control because with a high positive peak voltage applied to the grid, the resulting grid rectification produces a large negative bias, by charging grid bias capacitor 22, which is highly desirable and useful in preventing false operation of the thyratrons in response to extraneous signals such as fluctuations in supply voltage.

For increases in the direct currents flowing in the saturated winding to 2 milliamperes, 3 milliamperes and 4 milliamperes, the voltages induced in the secondary winding are correspondingly advanced in phase as represented by the curves 21, 2B and 29. It will be noted that throughout the phase shifting range the phase shifted voltage has the desirable characteristics mentioned in the foregoing, i. e. steep wave front high positive peak, high negative values, positive half cycle approximately negative half cycle approximately 270.

In an embodiment which gives very satisfactory operation, the elements have the values listed in the following table:

Resistor ll "ohms-.. 20,000 Resistor 12a do 5,000 Resistor 24 do 1,000 Capacitor 10 "ma- 1.0 Capacitor 12 mf .5 Capacitor 22 mi..- .1 Resistor 19 --megohm .5 Resistor 20 do .5 Resistor 21 do 1.0

The unsaturated reactance of saturable core reactor 9 is equal to approximately four times the reactance of capacitor W.

In a modified form, the resistor II and the capacitor l2 are omitted. A series filter comprising an inductance 30 and a capacitor 3| is connected in the output circuit of the bridge, as indicated in Fig. 3.

Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the elements shown and described are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An apparatus for producing a peaked voltage suitable for grid control of gaseous discharge devices and variable in phase with respect to a periodically varying voltage comprising a, pair of inductors in adjacent arms of a bridge circuit configuration, a capacitive reactance element and the reactance winding of a saturable reactor connected in series to form a third arm of said bridge, a resistance and a capacitor connected in parallel to form the fourth arm of said bridge, a pair of transformers having their primary windings connected in series across the diagonal of said bridge circuit, a pair of oppositely poled rectifiers connected across said primary windings, each of said rectifiers being connected in parallel with a corresponding one of said primary windings to provide for alternately short-circuiting one of said windings during each half wave of. voltage across said windings thereby to induce in the transformer secondar windings unsymmetrical voltages of which positive half cycles are of relatively short duration and negative half cycles are of relatively long duration.

2. A circuit for producing a phase shiftable voltage of peaked wave form suitable for the control of grid controlled gaseous discharge devices comprising a pair of transformer secondary windings in adjacent arms of a bridge circuit configuration, a saturable reactor and a capacitive reactance element connected in series relationship to form a third arm of said bridge, said reactance element comprising a first capacitor and a. re-- sistor connectedin parallel with each other, a second resistor and a second capacitor connected in parallel relationship with each other to provide the fourth arm of said bridge, two additional transformers having their primary windings connected in series across the diagonal of said bridge between the junction point of said secondary windings and the junction point of said third and fourth arms and two rectifiers each connected respectively in parallel with one of said primary windings for causing the periodically varying voltages induced in the secondary windings of said additional transformers to be unsymmetrical about the zero axis with negative half cycles of relatively greater duration than the positive half cycles.

3. An apparatus for producing an unsymmetrical voltage variable in phase with respect to the voltage of a source of periodically varying voltage comprising a transformer having a primary winding connected to said source of periodically varying voltage, a pair of secondary windings on said transformer connected as adjacent arms in 25 a bridge circuit configuration, a capacitor and the reactance winding of a saturable reactor connected in series to form a third arm of said bridge configuration, the reactance of said reactor winding being variable between a minimum value and a maximum value which is equal to approximately four times the reactance of said capacitor, a resistor and capacitor connected in parallel to form the fourth arm of said bridge, oppositely poled rectiflers connected in series across the diagonal of said bridge between the junction point of said transformer secondary windin and the junction point of said third and fourth adjacent arms, third and fourth transformers having their primary windings connected in series across the diagonal of said bridge, and a resistor connected between the junction point of said rectifiers and the junction point of said third and fourth transformer primary windings.

DANIEL F. LANGENWALTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,893,772 Garman Jan. 10, 1933 1,900,538 I Bedford Mar. 7, 1933 1,926,275 Fitz Gerald Sept. 12, 1933 2,084,900 Edwards June 22, 1937 2,228,843 Palmer Jan. 14, 1941 2,246,177 Levoy June 17, 1941

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